That's a touchy subject among DIYers. Seen a lot of fighting between gram-ers and the ml-ers.I personally use syringes and can mix up a recipe and clean up in very little time. I have also mixed by weight but prefer by volume.

I'm a ML'r hybrid.

I measure once using ML's and mix a 1000 times.

I just measure out my nic for the size bottle I'm filling. I then make a permanent mark on the bottle with a Sharpie.The flavoring I count the drops (can write it on the side of the bottle)The PG and VG are done by eye in the 60/40 - 70/30 range.

If it works don't fix it. Honestly you can't mix any easier then that.

1) Measure the proper volume of nicotine base2) Add flavoring/s by volume3) Fill the rest of the bottle with premixed PG/VG 50:50.

If a person mixes 100 ml at a time and use 100 mg/ml base, the calculations are trivial:

The ml of base needed is the same as the desired mg/ml solution - so if you want 24 mg/ml juice, you put 24 ml of base in the bottle.

The amount of flavoring is equal to the percentage of flavoring desired. So if you want 3% of one flavor and 2% of a second, you add 3 ml of the first flavor and 2 ml of the second flavor to the bottle.

Using the premixed PG/VG, fill the rest of the bottle with the PG/VG mixture.

Of course, this ignores the carriers for the nicotine base and flavors. I buy my nicotine base premixed 50:50 PG/VG. I only use a few percent total of flavorings, so ignore its contribution to the PG total.